1. Field of the Invention
This invention relates to diesel fuels, more particularly, to diesel fuels compositions containing an additive composition made by admixing at least one dicarboxylic acid, at least one amine and optionally at least one monocarboxylic acid.
2. Description of the Related Art
Low sulfur diesel fuel, defined as having up to 0.05% by weight sulfur content, has been required by law in the U.S. for on-highway use since October 1993 and in Europe since October 1996. Other nations in the Americas and Asia have timetables in place to follow suit. The driving force to low sulfur diesel fuel is the desire to minimize harmful emissions from diesel vehicles. Scientific evidence exists linking diesel fuel sulfur levels to particulate matter emissions from diesel vehicles.
Diesel fuel sulfur level is reduced by hydrotreatment of various distillate streams at the refinery. Hydrotreatment not only removes sulfur, but also removes other polar compounds and polycyclic aromatic compounds normally present in the diesel fuel. These compounds contribute to the natural lubricity of diesel fuel. When these compounds are removed during the hydrotreatment process, the final low sulfur diesel fuel tends to have poor natural lubricity.
Light duty diesel engines are usually fitted with rotary type fuel injection pumps. These pumps are lubricated only by the diesel fuel. Low sulfur fuels having poor natural lubricity have been shown to cause wear in these pumps leading to troublesome operation and premature pump failure. The use of lubricity additives in low sulfur diesel fuels has been shown to reduce or prevent pump wear.
Engine oil contacts diesel fuel in certain types of in-line diesel injection pumps and through direct addition of used engine oil to the fuel. Certain types of lubricity additives used in low sulfur diesel fuel have been found to contribute to fuel filter blockage and to pump plunger sticking. Lubricity additives having poor compatibility with engine oil have been shown to cause these problems. Poor compatibility means that the diesel fuel containing the lubricity additive tends to form fuel insoluble deposits, gels, or heavy sticky residues when in contact with engine oil. These deposits, gels or residues have been shown to cause fuel filter blockage and injection pump sticking.
It would be advantageous to provide a diesel fuel composition that has enhanced lubricity characteristics and is compatible with engine oil. The present invention provides such an advantage. The diesel fuel compositions of the present invention, in addition to having enhanced antiwear performance also have increased storage stability, and enhanced antirust performance.
Japanese laid-open Patent Publication No 8-134476, Takizawa, May 28, 1996, discloses a low sulfur diesel fuel composition, comprising a low sulfur diesel fuel having a sulfur content of 0.05% by weight, and 5-500 mg/L of at least one of a dicarboxylic acid salt of an alkylene diamine, said dicarboxylic acid having a saturated or unsaturated hydrocarbon group of 5-28 carbon atoms and said alkylene diamine having one amino group substituted by a saturated or unsaturated hydrocarbon group of 5-28 carbon atoms; a monocarboxylic acid salt of an alkylene diamine, said monocarboxylic acid having a saturated or unsaturated hydrocarbon group of 5-28 carbon atoms; and a carboxylic acid salt of a monoamine, said carboxylic acid having a saturated or unsaturated hydrocarbon group of 5-28 carbon atoms and said monoamine having a saturated or unsaturated hydrocarbon group of 5-28 carbon atoms. This composition is disclosed to provide excellent anti-wear property and excellent sliding property.